Method for transmitting and receiving system information elements in a wireless access system

ABSTRACT

A method for configuring system information, a method for transmitting system information, and a method for transmitting resource ratio information are disclosed. A method for receiving system information elements includes receiving a first message including a fixed-size system information element from a base station, and receiving a second message including an variable-size system information element from the base station.

CROSS REFERENCE TO RELATED APPLICATIONS

This application Application is a Reissue Continuation of U.S. Reissuepatent application Ser. No. 14/481,651 filed on Sep. 9, 2014 (now U.S.Pat. No. RE45,996 issued on May 3, 2016), which is a Reissue of U.S.Pat. No. 8,547,926 issued on Oct. 1, 2013, which is the National Phaseof PCT/KR2009/001009 filed on Mar. 2, 2009 which claims priority under35 U.S.C 119(e) of U.S. Provisional Application No. 61/033,011 filed onMar. 2, 2008. The entire contents of the above applications are herebyincorporated by reference into the present application. Notice: Morethan one reissue application has been filed for the reissue of U.S. Pat.No. 8,547,926: U.S. patent application Ser. No. 14/593,936 (presentapplication) and U.S. patent application Ser. No. 14/481,651.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless access system, and moreparticularly, to a method for configuring system information and amethod for transmitting system information, when a subframe structure isused. The present invention also relates to a method for notifyingresource ratio information, when a subframe structure is used.

2. Discussion of the Related Art

A typical frame structure used in a wireless access system will bedescribed below.

FIG. 1 illustrates a frame structure in a broadband wireless accesssystem (e.g. Institute of Electrical and Electronics Engineers (IEEE)802.16).

Referring to FIG. 1, the horizontal axis represents Orthogonal FrequencyDivision Multiple Access (OFDMA) symbols as time units and the verticalaxis represents the logical numbers of subcarriers as frequency units,in a frame. One frame is divided into data sequence channels each havinga predetermined duration according to the physical characteristics ofthe data sequence channels. Specifically, a frame is divided into aDownLink (DL) subframe and an UpLink (UL) subframe. A Transmit/receiveTransition Gap (TTG) is interposed between a DL subframe and a ULsubframe and a Receive/transmit Transition Gap (RTG) is interposedbetween frames.

A DL subframe may carry a preamble, a Frame Control Header (FCH), aDL-MAP, a UL-MAP, and one or more DL data bursts. A UL subframe maycarry one or more UL data bursts and a ranging subchannel.

The preamble is a predetermined data sequence residing in the firstsymbol of each frame, for use in a Mobile Station's (MS's) acquisitionof synchronization with a Base Station (BS) and channel estimation. TheFCH provides information about channel allocation and channel coding ofthe DL-MAP. The DL-MAP and the UL-MAP are Media Access Control (MAC)messages carrying channel resource assignments to MSs. The DL databursts and the UL data bursts are data units that the BS transmits toMSs or MSs transmit to the BS, respectively.

A Downlink Channel Descriptor (DCD) that can be transmitted in the framestructure illustrated in FIG. is a MAC message describing the physicalcharacteristics of a downlink channel and an Uplink Channel Descriptor(UCD) is a MAC message describing the physical characteristics of anuplink channel.

On a downlink, an MS may detect a preamble transmitted from a BS andthen decode a DL-MAP using information acquired from an FCH. The BS maytransmit scheduling information to MSs in every frame (e.g. every 5 ms)by a DL-MAP or UL-MAP message to allocate downlink or uplink resourcesto the MSs.

[Table 1] below illustrates an exemplary format of the DL-MAP message.

TABLE 1 Size Syntax in bits Description DLMAP_Message_Format( ){ — — Management Message Type  8 — = 2  PHY Synchannel Field Variable seeappropriate PHY sepcification.  DCD Count  8 —  Base station ID 48 — Begin PHY-specific — see applicable PHY subclause section{  if(Wireless MAN- — — OFDMA){     No.OFDMA symbols  8 Number of OFDMAsymbols in the DL subframe including all AAS/permutation zone andincluding the preamble   } } }   for(i=1; i<=n; i++){ — For each UL-MAPelement 1 to n.     DL-MAP_IE( ) variable See corresponding PHYspecification   } — —  } — —  if!(byte boundary){ — —   Padding Nibble 4 Padding to reach byte boundary  } — — } — —

Referring to [Table 1], Management Message Type is 2, identifying aDL-MAP message. A DCD provides downlink channel information (e.g.downlink burst profiles). DCD Count field specifies a value of theConfiguration Change Count of the DCD. Hence, DCD Count field mayindicate whether the DCD has been changed. No. OFDMA symbols filedspecifies the number of OFDMA symbols allocated to a DL subframe. TheDL-MAP message may include a variety of DL-MAP Information Elements(IEs) (i.e. DL-MAP_IE( ).

[Table 2] below illustrates an exemplary format of the UL-MAP message.

TABLE 2 Size Syntax in bits Description UL-MAP_Message_Format( ){ — — Management Message Type  8 — = 3  Reserved  8 Shall be set to zero  UCDCount  8 —  Allocation Start Time 32 —  Begin PHY-specific — seeapplicable PHY sub- section{ clause   if(Wireless MAN- — — OFDMA){   No.OFDMA symbols  8 Number of OFDMA symbols in the UL sub- frame   }— —   for(i=1; i<=n; i++){ — For each UL-MAP element 1 to n.   UL-MAP_IE( ) variable See corresponding PHY specification   } — —  }— —  if!(byte boundray){ — —   Padding Nibble  4 Padding to reach byteboundary  } — — } — —

Referring to [Table 2], Management Message Type is 3, identifying aUL-MAP message. A UCD provides uplink channel information (e.g. uplinkburst profiles). UCD Count field specifies a value of the ConfigurationChange Count of the UCD. Hence, UCD Count field may indicate whether theUCD has been changed. Allocation Start Time specifies an effective starttime of uplink allocation defined by the UL-MAP message, in PHY-specificunits. No. OFDMA symbols field specifies the number of OFDMA symbolsallocated to a UL subframe.

In a Wireless Metropolitan Area Network-Orthogonal Frequency DivisionMultiple Access (WMAN-OFDMA) system, a BS may transmit most of systemIEs (or system configuration information) to MSs periodically (e.g.every 0.5 to 2 seconds or every up to 10 seconds) via a DCD/UCD message.In addition, the BS may transmit certain system configurationinformation, such as a frame number, a frame duration, a BS Identifier(ID), the number of symbols, to the MSs via a MAP message.

In general, system IEs are transmitted with a long period and an MSneeds to acquire the system IEs in order to enter a network. Thus, thenetwork entry of the MS may take a long time. In addition, since systeminformation carried in a DL-MAP does not change often, it is notnecessary to transmit the system information in every frame.

System information delivered by a DCD/UCD takes the form of Type,Length, and Value (TLV). Accordingly, additional information such asType and Length is required for a specific system IE, thus consumingresources. The length of a message is actually determined based on TLVencoding information of system IEs included in the message. Therefore,the BS should notify an MS of the size of resources occupied by themessage all the time.

A system IE may be transmitted at a fixed size. Because the system IEincludes information of a fixed size, the BS does not need to transmitresource allocation information about the Type and Length fields of thesystem IE to MSs. If all system IEs are used at fixed sizes, thescalability of the system IEs may be decreased. Moreover, all systeminformation delivery messages are transmitted at fixed sizes every fixedperiod and thus more radio resources are used to transmit systeminformation.

If the BS transmits a system information delivery message includingsystem IEs of fixed sizes every predetermined period, which is longerthan a superframe period (e.g. a multiple of the superframe period, suchas 40 ms, 80 ms, etc.), less resources may be used than when systeminformation is transmitted every superframe period. However, theproblems of decreased scalability and delayed initial network entry ofMSs still exist.

One system IE used in a WMAN-OFDMA Time Division Duplexing (TDD) system(e.g. IEEE 802.16d/e/Rev2) is a DL/UL ratio field indicating the ratiobetween DL subframes and UL subframes (or No. OFDMA symbols).

The DL/UL ratio field may be included in the DL-MAP and UL-MAP messages.Once a DL/UL ratio is set, the system does not change the DL/UL ratiooften. Especially if information about the configuration and/or length(e.g. the number of Orthogonal Frequency Division Multiplexing (OFDM)symbols) of a subframe can be acquired from system information in asystem using superframe and subframe structures, it is a waste of radioresources to transmit DL/UL ratio information on a symbol basis.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method fortransmitting system information that substantially obviates one or moreproblems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a method fortransmitting system IEs efficiently.

Another object of the present invention is to provide a configuration ofsystem IEs and a structure of a system information delivery message totransmit system IEs.

Another object of the present invention is to provide a method forefficiently transmitting fixed system IEs or variable system IEs.

A further object of the present invention is to provide a method fortransmitting a DL/UL ratio field and a structure of the DL/UL ratiofield.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod for receiving system information elements includes receiving afirst message including a fixed-size system information element from abase station, and receiving a second message including an variable-sizesystem information element from the base station.

The first message may further include configuration information aboutthe variable-size system information element.

The first message may be a primary superframe header and the secondmessage may be a secondary superframe header. The first message may betransmitted in every superframe and the second message may betransmitted every predetermined number of superframes.

The first message may be a superframe header and the second message maybe one of a subframe header, a downlink channel descriptor message, andan uplink channel descriptor message. If the fixed-size systeminformation element is changed, the second message may include a changedfixed-size system information element.

The first message may further include downlink to uplink ratio (DL/ULratio) information.

In another aspect of the present invention, a method for transmittingsystem information elements includes transmitting a first messageincluding a fixed-size system information element to a mobile station,and transmitting a second message including a variable-size systeminformation element to the mobile station.

The first message may further include configuration information aboutthe variable-size system information element. The first message may be aprimary superframe header and the second message may be a secondarysuperframe header. The first message may be transmitted in everysuperframe and the second message may be transmitted every predeterminednumber of superframes.

The first message may be a superframe header and the second message maybe one of a subframe header, a downlink channel descriptor message, andan uplink channel descriptor message. If the fixed-size systeminformation element is changed, the second message may include a changedfixed-size system information element.

The first message may further include downlink to uplink ratio (DL/ULratio) information.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates a frame structure in a broadband wireless accesssystem (e.g. Institute of Electrical and Electronics Engineers (IEEE)802.16).

FIG. 2 illustrates a new frame structure used in exemplary embodimentsof the present invention.

FIG. 3 illustrates a configuration of downlink subframes and uplinksubframes used in exemplary embodiments of the present invention.

FIG. 4 illustrates configurations of system information according toexemplary embodiments of the present invention.

FIG. 5 illustrates transmission of a system information delivery messageaccording to an exemplary embodiment of the present invention.

FIG. 6 illustrates frame structures based on resource allocationinformation according to exemplary embodiments of the present invention.

FIG. 7 illustrates signal flows for methods for transmitting systeminformation according to exemplary embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a wireless access system. Exemplaryembodiments of the present invention provide various methods forconfiguring system information and various methods for transmittingsystem information. In addition, the exemplary embodiments of thepresent invention provide various methods for transmitting resourceratio information (e.g. a DownLink/UpLink (DL/UL) ratio field).

The exemplary embodiments of the present invention described hereinbeloware combinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an exemplaryembodiment of the present invention may be constructed by combiningparts of the elements and/or features. Operation orders described inembodiments of the present invention may be rearranged. Someconstructions of any one embodiment may be included in anotherembodiment and may be replaced with corresponding constructions ofanother exemplary embodiment.

In the description of drawings, procedures or steps, which may distractfrom the substance of the present invention, are not explained. Inaddition, procedures or steps, which can be understood by those skilledin the art, are not explained as well.

In the exemplary embodiments of the present invention, a description ismade of a data transmission and reception relationship between a BaseStation (BS) and a Mobile Station (MS). Herein, the term ‘BS’ refers toa terminal node of a network, which communicates directly with the MS.In some cases, a specific operation described as performed by the BS maybe performed by an upper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with an MS may be performed by the BS, or network nodesother than the BS. The term ‘BS’ may be replaced with the term ‘fixedstation’, ‘Node B’, ‘eNode B (eNB)’, ‘access point’, etc. The term usedherein ‘MS’ may be replaced with the term ‘User Equipment (UE)’,‘Subscriber Station (SS)’, ‘Mobile Subscriber Station (MSS)’,‘terminal’, ‘mobile terminal’, etc.

A transmitter means a fixed and/or mobile node that transmits voice ordata service and a receiver means a fixed and/or mobile node thatreceives voice or data service.

Hence, an MS may be a transmitter and a BS may be a receiver, on anuplink. Likewise, the MS may be a receiver and the BS may be atransmitter, on a downlink.

Meanwhile, the MS may be any of a Personal Digital Assistant (PDA), acellular phone, a Personal Communication Service (PCS) phone, a GlobalSystem for Mobile (GSM) phone, a Wideband Code Division Multiple Access(WCDMA) phone, a Mobile Broadband System (MBS) phone, a hand-held PC, alaptop PC, a smart phone, a Multi Mode-Multi Band (MM-MB) terminal, etc.

Smart phones combine the functions of both mobile phones and PDAs, suchas, scheduling and data communications such as fax transmission andreception and Internet connection. The MB-MM terminal refers to aterminal which has a multi-modem chip therein and which can operate inany of a mobile Internet system and other mobile communication systems(e.g. CDMA 2000, WCDMA, etc.)

Exemplary embodiments of the present invention may be achieved byvarious means, for example, hardware, firmware, software, or acombination thereof.

In a hardware configuration, the methods according to embodiments of thepresent invention may be achieved by one or more Application SpecificIntegrated Circuits (ASICs), Digital Signal Processors (DSPs), DigitalSignal Processing Devices (DSPDs), Programmable Logic Devices (PLDs),Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, etc.

In a firmware or software configuration, the methods according to theexemplary embodiments of the present invention may be implemented in theform of a module, a procedure, a function, etc. performing functions oroperations as set forth herein. Software code may be stored in a memoryunit and executed by a processor. The memory unit is located at theinterior or exterior of the processor and may transmit and receive datato and from the processor via various known means.

The exemplary embodiments of the present invention are supported bystandard documents disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802 system, a 3^(rd) Generation Project Partnership (3GPP) system, a3GPP Long Term Evolution (LTE) system, and a 3GPP2 system. Inparticular, the steps or parts, which are not described to clearlyreveal the technical idea of the present invention, in the exemplaryembodiments of the present invention may be supported by the abovedocuments. All terms used in the exemplary embodiments of the presentinvention may be explained by the standard documents. Especially theexemplary embodiments of the present invention may be supported by atleast one of P802.16e-2004, P802.16e-2005, and P802.16Rev2 documentswhich are the standards of IEEE 802.16.

Reference will now be made in detail to the preferred embodiments of thepresent invention with reference to the accompanying drawings. Thedetailed description, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present invention, rather than to show the only embodiments that canbe implemented according to the invention.

Specific terms used for the embodiments of the present invention areprovided to help the understanding of the present invention. Thesespecific terms may be replaced with other terms within the scope andspirit of the present invention.

For example, a system information delivery message may also be referredto as a SuperFrame Header (SFH), a broadcast channel (BCH) or anadditional system information message.

FIG. 2 illustrates a new frame structure used in exemplary embodimentsof the present invention.

Referring to FIG. 2, one superframe may include one or more frames andeach frame may include one or more subframes. Each subframe may includeone or more Orthogonal Frequency Division Multiple Access (OFDMA)symbols.

The lengths and numbers of superframes, frames, subframes and symbolsmay be adjusted according to a user request or a system environment.Herein, the term ‘subframe’ refers to any lower-layer frame structureproduced by dividing one frame by a predetermined length.

In FIG. 2, it is assumed that a superframe is 20 ms long and a frame is5 ms long. Each frame may include 8 subframes, each subframe having 6OFDMA symbols. The specific values may vary depending on channelenvironments.

An SFH may reside at the start of each superframe (i.e. first, secondand third OFDMA symbols of the superframe) in order to deliver physical(or logical) channel information (or system information) of the systemsuch as frame configuration information. The SFH may be referred to as aSuper MAP, a broadcast channel (BCH) (or broadcast control channel(BCCH)), a common control channel (CCCH) or a superframe-MAP.Hereinafter, the term ‘SFH’ is used in the exemplary embodiments of thepresent invention.

A subframe MAP may be allocated to the start of a subframe. The subframeMAP may also be referred to as a Sub-MAP or Advanced-MAP (A-MAP). TheSub-MAP may include a DL-Sub-MAP and a UL-Sub-MAP.

FIG. 3 illustrates a configuration of downlink subframes and uplinksubframes used in exemplary embodiments of the present invention.

Referring to FIG. 3, different numbers of DL subframes and UL subframesform a Time Division Duplexing (TDD) frame. The DL:UL ratio is 5:3herein. This means that if one frame includes 8 subframes, 5 subframesout of the 8 subframes are DL subframes and the other 3 subframes are ULsubframes.

<Method for Configuring System Information Delivery Message>

In accordance with an exemplary embodiment of the present invention, asystem information delivery message may be divided into a fixed-sizepart and a variable-size part to transmit system informationefficiently. The system information delivery message may be an SFH inexemplary embodiments of the present invention. The fixed-size part andvariable-size part of the system information delivery message may bereferred to as a primary SFH and a secondary SFH, respectively.

The primary SFH may be transmitted at a fixed MCS level with a fixedconfiguration every SFH period. Because system IEs have fixed sizes inthe primary SFH, the system IEs are preferably limited in size. That is,the system IEs included in the primary SFH always have fixed sizes andthus need not be represented in the form of Type, Length, Value (TLV).

The configuration of the secondary SFH may be considered in two ways.For example, the secondary SFH may be designed so as to include systemIEs of one type. The type of system IEs included in the secondary SFHmay vary from one wireless communication system to another. The systemIEs included in the secondary SFH may be defined by each wirelesscommunication system.

In addition, the secondary SFH may be designed such that system IEs ofone or more types are available to the secondary SFH and differentsystem IEs may be included in the secondary SFH according to the typesof system IEs. According to the type of system IEs included in thesecondary SFH, the secondary SFH may be transmitted with a differenttransmission period. In this case, preset system IEs may be included inthe secondary SFH all the time according to the type of system IEs.Therefore, each message need not be represented in the form of TLV.

Criteria to distinguish between system IEs for a primary SFH and systemIEs for a secondary primary SFH in a system information delivery message(e.g. an SFH) according to exemplary embodiments of the presentinvention will be described below.

According to one criterion, frame configuration information, framecontrol information, and primary IEs required for initial network entryof MSs may be included in the primary SFH.

The frame control information may include a Frame Number field, aReceive/transmit Transition Gap (RTG), a Transmit/receive Transition Gap(TTG), the number of symbols of a DL subframe, a UL allocation starttime, a BS Identifier (ID), etc.

The primary IEs may include a ranging code (e.g. an initial rangingcode, a periodic ranging code, a handover ranging code and/or abandwidth request ranging code), backoff start/end values, a rangingregion according to the ranging code, an initial value of the rangingcode, a permutation base, UL initial transmit timing information, etc.System IEs other than the system IEs included in the primary SFH, suchas handover information, may be included in the secondary SFH.

The other criterion is that among the frame configuration informationand the primary IEs required for network entry, system IEs that arerarely changed are included in the primary SFH and system IEs that arehighly likely to change are included in the secondary SFH.

FIG. 4 illustrates configurations of system information according toexemplary embodiments of the present invention.

Referring to FIG. 4(a), system IEs may be configured with fixed-sizesystem information (or fixed system information) 410 and variable-sizesystem information (or variable system information) 430. In theexemplary embodiments of the present invention, the fixed-size systeminformation 410 may be referred to as a primary SFH and thevariable-size system information 430 may be referred to as a secondarySFH.

The primary SFH 410 may include Configuration Information (CI) 420 thatprovides physical (or logical) information about the secondary SFH 430.The CI 420 may include an indicator indicating whether the secondary SFH430 is included, an Information Type field indicating the type of systemIEs included in the secondary SFH 430, and a Version field indicatingthe version of the system IEs included in the secondary SFH 430. The CI420 may further include a Resource Allocation field and a Resource BlockSize field, which specify a region to which the secondary SFH 430 isallocated.

Referring to FIG. 4(b), system information may include the fixed-sizesystem information (i.e. the primary SFH) 410, the CI 420, and thevariable-size system information (i.e. the secondary SFH) 430. Thesystem information configuration illustrated in FIG. 4(b) differs fromthat illustrated in FIG. 4(a) in that the CI 420 is transmittedseparately from the primary SFH 410. The CI 420 may carry the sameconfiguration information about the secondary SFH 430 as described abovewith reference to FIG. 4(a).

FIG. 5 illustrates transmission of a system information delivery messageaccording to an exemplary embodiment of the present invention.

Referring to FIG. 5(a), a primary SFH may be transmitted at the start ofeach superframe. While the primary SFH may be transmitted in everysuperframe, a secondary SFH may be transmitted in every othersuperframe. CI may be included in the primary SFH and the CI may includeinformation about the secondary SFH, such as an information elementindicator and an Information Type field.

Variable system IEs included in the secondary SFH may be of one type. Inthis case, the CI may be transmitted in the primary SFH in everysuperframe. The information element indicator included in the CI mayindicate whether the secondary SFH is included in the superframe.

FIG. 5(b) illustrates a system information delivery message in whichvariable system IEs of one or more types are included in the secondarySFH. In this case, the size of the secondary SFH may be changed in everysuperframe. For example, the Information Type field of the CI mayindicate a first type in an N^(th) superframe, a second type in an(N+1)^(th) superframe, and a third type in an (N+2)^(th) superframe.That is, the size of the secondary SFH may be changed according to thetype of system IEs included in the secondary SFH in every superframe. Inthe illustrated case of FIG. 5(b), the indicator included in the CI inan (N+3)^(th) superframe indicates that the secondary SFH is notincluded in the (N+3)^(th) superframe.

<Method for Transmitting DL/UL Ratio Information>

In a communication system, DL/UL ratio information does not changeoften. Hence, there is no need to transmit DL/UL ratio information inevery frame. Especially when an MS determines the configuration and/orlengths of subframes (for example, the length of a subframe is expressedas the number of OFDM symbols in the subframe) from system IEs in asystem using superframe and subframe structures, transmission of DL/ULratio information on a symbol basis from a BS may lead to waste of radioresources.

In accordance with another exemplary embodiment of the presentinvention, the BS may transmit DL/UL ratio information to the MS on asubframe basis. Referring to FIG. 3, one frame may include 8 subframes.The BS may transmit DL/UL ratio information in the form of a bitmap oran index based on a DL/UL pattern to the MS.

[Table 3] below illustrates an exemplary format of DL/UL ratioinformation taking the form of an 8-bit bitmap.

TABLE 3 Name Size Note DL/UL 8 DL/UL ratio and DL/UL switching point ina frame. ratio Each bit is mapped to one subframe and indicates whetherthe corresponding subframe is for downlink or uplink. If a bit for asubframe is 0, the subframe is for downlink traffic. Otherwise, thesubframe is for uplink.

Referring to [Table 3], if DL/UL ratio information is configured in theform of an 8-bit bitmap, each bit of the bitmap may be mapped to asubframe. For instance, Bit #7 (Most Significant Bit (MBS)) representsthe first subframe, Bit #6 represents the second subframe, and Bit #5represents the third subframe. In the same manner, Bit #0 (LeastSignificant Bit (LSB)) represents the last subframe, that is, the eighthsubframe.

In [Table 3], each bit of the bitmap may indicate whether a subframemapped to the bit is a downlink subframe or an uplink subframe. Forexample, if the bit is set to ‘0’, this indicates a downlink subframeand if the bit is set to ‘1’, this indicates an uplink subframe. In thismanner, the DL/UL ratio information may implicitly indicate thepositions and number of DL/UL switching points.

[Table 4] below illustrates an exemplary format of DL/UL ratioinformation taking the form of an index.

TABLE 4 Name Size Note DL/UL ratio 3 Each value indicates a DL/UL ratiodefined by the system. 0b000: (DL):(UL) = 5:3 0b001: (DL):(UL) = 6:20b010: (DL):(UL) = 4:4 0b011: (DL):(UL) = 2:2:2:2 0b100: (DL):(UL) = 3:50b101~0b111: reserved

In the exemplary embodiments of the present invention, DL/UL ratioinformation may be configured based on DL/UL ratios preset by thesystem. The DL/UL ratios may vary depending on a communicationenvironment or a user request. Referring to [Table 4], 0b000 indicates aDL/UL ratio of 5:3, 0b001 indicates a DL/UL ratio of 6:2, 0b010indicates a DL/UL ratio of 4:4, 0b100 indicates a DL/UL ratio of 3:5,and the other values are reserved for other DL/UL ratios.

In accordance with another exemplary embodiment, the BS may notify theMS of a frame structure using DL/UL ratios described above withreference to [Table 3] and [Table 4]. Once DL/UL ratio information isset, it cannot be changed easily. For example, therefore, the BS maytransmit the DL/UL ratio information to the MS by a primary SFHdescribed in FIG. 4. If a DL/UL ratio is changed for a frame, the BS maytransmit a Sub-MAP (or A-MAP) including the changed DL/UL ratioinformation to the MS. In this manner, the BS can indicate a changedDL/UL ratio to the MS.

FIG. 6 illustrates frame structures based on resource allocationinformation according to exemplary embodiments of the present invention.

FIG. 6(a) illustrates a frame structure having a DL/UL ratio of 5:3 fora frame. The BS may transmit DL/UL ratio information (e.g. 0b00000111)using a bitmap having the configuration of [Table 3] to the MS, ortransmit DL/UL ratio information (e.g. 0b000) using an index illustratedin [Table 4] to the MS.

Referring to FIG. 6(a), a DL/UL switching point is a transition betweena bit value 0 to a bit value 1 or vice versa. In the illustrated case ofFIG. 6(a), a frame has two DL/UL switching points (i.e. a TTG and anRTG), between the fifth and sixth subframes of the frame and between thelast subframe of the frame and the first subframe of the next frame.

FIG. 6(b) illustrates a frame structure having a DL/UL ratio of 2:2:2:2for a frame. The BS may transmit DL/UL ratio information (e.g.0b00110011) using a bitmap having the configuration of [Table 3] to theMS, or transmit DL/UL ratio information (e.g. 0b011) using an indexillustrated in [Table 4] to the MS.

In FIG. 6(b), four DL/UL switching points (TTGs and RTGs) are defined ina frame. Specifically, TTGs are interposed between the second and thirdsubframes of the frame and between the sixth and seventh subframes ofthe frame, and RTGs are interposed between the fourth and fifthsubframes of the frame and between the last subframe of the frame andthe first subframe of the next frame.

FIG. 7 illustrates signal flows for methods for transmitting systeminformation according to exemplary embodiments of the present invention.

Referring to FIG. 7(a), the BS may transmit a primary SFH includingfixed system IEs and CI to the MS. The fixed system IEs and CI have beendescribed before with reference to FIG. 4. The fixed system IEs mayinclude DL/UL ratio information described with reference to FIG. 6(S710).

The CI provides configuration information about a secondary SFH. Inanother exemplary embodiment, the BS may transmit the CI to the MS usinga separate message, as opposed to transmitting the CI in the primary SFHin step S710.

The BS may transmit a secondary SFH including variable system IEs to theMS (S730). The variable system IEs are IEs that may be changed in thesystem, except the fixed system IEs.

Referring to FIG. 7(b), the BS may transmit fixed system IEs to the MSby a system information delivery message such as an SFH, a Super MAP ora BCH. That is, the BS may transmit the fixed system IEs using an SFHthat is transmitted in every superframe (every 20 ms). The fixed systemIEs may include DL/UL ratio information described with reference to FIG.6 (S720).

In addition, the BS may transmit variable system IEs to the MS by anadditional system information delivery message such as a DCD message, aUCD message, a Sub-MAP, or an A-MAP (S740).

Depending on a communication environment or a user request, the fixedsystem IEs allocated in step S720 may have been changed. In this case,the BS may transmit the changed system IEs to the MS via a DCD message,a UCD message, a SubMAP, or an A-MAP (S760).

In FIG. 7(b), the BS may transmit the DL/UL ratio information to the MSvia a DCD message or the like, not via an SFH. In this case, the DCDmessage is not transmitted every superframe period and thus it takes along time for the MS to acquire the DL/UL ratio information. Morespecifically, when the DL/UL ratio information is transmitted in aprimary SFH or an SFH, the MS may acquire the DL/UL ratio informationfaster than when the DL/UL ratio information is transmitted in asecondary SFH or a DCD/UCD message.

Now a description will be given of apparatuses of an MS and a BS thatcan implement the exemplary embodiments of the present inventionillustrated in FIGS. 2 to 7 according to an exemplary embodiment of thepresent invention.

The MS may operate as a transmitter on an uplink and as a receiver on adownlink. The BS may operate as a receiver on the uplink and as atransmitter on the downlink. Therefore, the MS and the BS may eachinclude a transmitter and a receiver to transmit and receive informationor data.

The MS and the bS may each include a processor, a module, a part and/ormeans to implement the exemplary embodiments of the present invention.Especially the MS and the BS may each include a module (means) forencrypting a message, a module for decrypting an encrypted message, andan antenna for transmitting and receiving messages.

The MS according to the exemplary embodiments of the present inventionmay include a low-power Radio Frequency/Intermediate Frequency (RF/IF)module. In addition, the MS may include means, modules or parts forperforming a control function, a MAC frame conversion control functionbased on service characteristics and a propagation environment, ahandover function, an authentication and encryption function, a packetmodulation and demodulation function for data transmission andreception, a high-speed packet channel coding function, and a real-timemodem control function in order to implement the above-describedexemplary embodiments of the present invention.

The BS may transmit data received from a higher layer to the MS in awireless or wired fashion. The BS may include a low-power RF/IF module.In addition, the BS may include means, modules or parts for performing acontrol function, OFDMA packet scheduling, TDD packet scheduling andchannel multiplexing, a MAC frame conversion control function based onservice characteristics and a propagation environment, a handoverfunction, an authentication and encryption function, a packet modulationand demodulation function for data transmission and reception, ahigh-speed packet channel coding function, and a real-time modem controlfunction in order to implement the above-described exemplary embodimentsof the present invention.

As is apparent from the above description of the exemplary embodimentsof the present invention, system information can be efficientlytransmitted.

Since a system information delivery message is divided into a primarySFH and a secondary SFH, the overhead of fixed-size system IEs can bereduced. The fixed-size system IEs do not include a Type field and aLength field, thereby reducing the overhead of the system informationdelivery message.

Radio resources can be conserved by transmitting a DL/UL ratio fieldfrom a BS. Furthermore, an MS can acquire DL/UL ratio information fromthe DL/UL ratio field in an SFH.

The exemplary embodiments of the present invention are applicable tovarious wireless access systems including a 3GPP system, a 3GPP2 system,and/or an IEEE 802.xx system. Besides these wireless access systems, theexemplary embodiments of the present invention are applicable to alltechnical fields to which wireless access systems are applied.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. It will be obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an exemplary embodiment of thepresent invention or included as a new claim by a subsequent amendmentafter the application is filed.

What is claimed is:
 1. A method for receiving system informationelements, in a wireless access system, the method comprising: receiving,by a mobile station (MS), a super frame header (SFH) including afixed-size system information element (IE) and configuration information(CI) related to a variable-size system information element (IE), whereinthe CI includes an information type field indicating a type of thevariable size system IE; and receiving, by the MS, an advanced-MAP(A-MAP) based on the CI, the A-MAP including the variable-size systeminformation element (IE), wherein the SFH is transmitted at a start ofeach superframe and the A-MAP is transmitted at a start of a downlink(DL) subframe included in a frame which is one of four frames includedin the superframe, the fixed-size system information element (IE)comprises at least one of a primary information element (IE) requiredfor initial network entry of the MS, frame configuration information,frame control information, and downlink to uplink ratio (DL/UL ratio)information indicating a ratio of DL subframes and UL subframes whichare included in each of the four frames, the variable-size systeminformation element (IE) has one or more types, and informationcomprised in the variable-size system information element (IE) isvariable according to the type indicated by the information type field,and the variable-size system information element (IE) further compriseschanged DL/UL ratio information if the DL/UL ratio information ischanged at the frame where the A-MAP is received.
 2. The methodaccording to claim 1, wherein the CI comprises an indicator indicatingwhether or not the A-MAP is present.
 3. The method according to claim 1,wherein the frame control information comprises a frame number field, areceive/transmit transition gap (RTG) field, a transmit/receivetransition gap (TTG) field, a number of symbols of a downlink subframe,an uplink allocation start time field, and a base station identifierfield.
 4. The method according to claim 1, wherein the primary IEcomprises at least one of ranging code information, backoff start valueinformation, backoff end value information, ranging region informationaccording to the ranging code information, permutation base information,and uplink initial transmit timing information.
 5. A method fortransmitting system information elements in a wireless access system,the method comprising: transmitting, by a base station (BS), a superframe header (SFH) including a fixed-size system information element(IE) and configuration information (CI) related to a variable-sizesystem information element (IE), wherein the CI includes an informationtype field indicating a type of the variable size system IE; andtransmitting, by the BS, an advanced-MAP (A-MAP) based on the CI, theA-MAP including the variable-size system information element (IE),wherein the SFH is transmitted at a start of each superframe and theA-MAP is transmitted at a start of a downlink (DL) subframe included ina frame which is one of four frames included in the superframe, whereinthe fixed-size system information element (IE) comprises at least one ofa primary information element (IE) required for initial network entry ofthe MS, frame configuration information, and frame control information,and downlink to uplink ratio (DL/UL ratio) information indicating aratio of DL subframes and UL subframes which are included in each of thefour frames, and wherein the variable-size system information element(IE) has one or more types, and information comprised in thevariable-size system information element (IE) is variable according tothe type indicated by the information type field, the variable-sizesystem information element (IE) further comprises changed DL/UL ratioinformation if the DL/UL ratio information is changed at the frame wherethe A-MAP is received.
 6. The method according to claim 5, wherein theCI comprises an indicator indicating whether or not the A-MAP ispresent.
 7. The method according to claim 5, wherein the frame controlinformation comprises a frame number field, a receive/transmittransition gap (RTG) field, a transmit/receive transition gap (TTG)field, a number of symbols of a downlink subframe, an uplink allocationstart time field, and a base station identifier field.
 8. The methodaccording to claim 5, wherein the primary IE comprises at least one ofranging code information, backoff start value information, backoff endvalue information, ranging region information according to the rangingcode information, permutation base information, and uplink initialtransmit timing information.
 9. A method of receiving a signal frame,the method comprising: receiving, by a receiving unit, a plurality ofOrthogonal Frequency Division Multiplexing (OFDM) symbols via anantenna; and processing, by a processor, the received plurality of OFDMsymbols, wherein the plurality of OFDM symbols are carried by a set offrame units, wherein at least one of the frame units includes a primarypart, a secondary part, and one or more sub-frames carrying data,wherein the primary part is followed by the secondary part, wherein theprimary part includes first system information of which size is fixed,wherein the secondary part includes second system information of whichsize is variable, and wherein the first system information includesinformation required to decode the secondary part, information toindicate a number of the sub-frames, and information to indicate anumber of OFDM symbols in a sub-frame.
 10. The method of claim 9,wherein the first system information further includes information on asize of the secondary part.